Generally, in order to know or determine if illustration, graphic design or any other type of business idea is profitable or not, you can check the figures/statistics (from government, industry associations etc) on what the businesses in any given country have been earning from selling such an idea over the last few years or so, this should tell you or let you know how profitable the idea has been over time, in a specific location or country.
However to determine if illustration/graphic design can be profitable specifically for you, you will need to do some research to
- Select a niche and targets to sell illustration/graphic design to
- Determine the value that will sell, that you can provide with illustration/graphic design to your chosen niche and targets
- Determine the uniqueness (or unique edge) that you will need to add to the value you will be providing with illustration/graphic design to your chosen niche and targets
- Test the demand for the value and the uniqueness you wish to provide with illustration/graphic design before you set it
up as a product/service to sell to your chosen niche/targets
- Determine how much it would potentially cost you, to make some specific amount of money with your illustrations/graphic designs as a product/service within a specific period of time
- Determine if you can afford to set up and sell the value and uniqueness you may want to provide with illustration/graphic design, as a product/service within that specific period of time
This is ideally what you should do with any idea (whether it is illustration, graphic design or any other idea that) you may want to sell as a product/service, if you wish to succeed with it, it is what will determine if the idea will be profitable specifically for you or not, you can learn more about this in The Profit Blueprint.